Mental Time Travel (MTT) refers to the ability to mentally simulate events that occur in times other than the present, and encompasses both remembering past events and imagining future ones. MTT is thought to be a uniquely human ability that plays a crucial role in self-control, emotion regulation, and decision-making, by linkng past experience with current feelings and future intention. The proposed research tests hypotheses derived from a new model of MTT and aging. In brief, the model predicts that the declines in episodic memory with age, combined with increases in motivation to regulate emotion, result in older adults constructing narratives of past, and possible future, events that have less sensory and perceptual detail (less episodic), but are more self-relevant and meaningful (more semantic). These meaning-rich narratives then decrease the current experience of negative affect and increase positive affect. Three experiments will be conducted to test these hypotheses. In each experiment, younger and older adults will be asked to describe events that did or might happen to them under different sets of instructions. Experiment 1 will test whether instructions that focus people on sensory and perceptual details of experiences paradoxically cause more negative moods. Experiment 2 will test whether instructions to maintain a positive mood will cause more semantically-based narratives. Experiment 3 will directly manipulate mood to determine if positive mood states cause decreases in the episodic nature of the described events.